I currently own a Vortex PST 2.5-10x32 FFP that I am very pleased with, but I am now looking to step up in magnification. I am considering both the 4-16x50 and the 6-24x50, but I am wondering how the quality of these models varies between the FFP and the SFP variants. I recall reading that the 2.5-10x44 SFP model, aside from the difference in focal plane, also had inferior glass compared to the 2.5-10x32 FFP. Do the SFP variants of the higher magnification models also have lower quality glass than the FFP variants? Are there any other significant differences (besides the obvious FFP vs SFP)?